How common should double/ triple yolkers be?

We seem to be getting 1-2 a week from our birds... near as we can tell, we have 2 girls that are laying them but we aren't sure who(darn work and stuff)... we have 8 hens right now( 2 2 year old Buff orps, A 1 year old black giant, and 5 1 year old orp/barred rock crosses)

yes they are common when they begin to lay, if they are still laying double and triple yolkers when they are older then they may be overweight but generally after the first 8 months or so of laying they should stop